Japan's July 30 yen buy was its biggest one-day intervention ever

Japan's Ministry of Finance dropped the receipts Monday: Tokyo bought yen on three days between July 30 and August 3, and the heaviest hit came first. On July 30 alone, authorities sold $50.36 billion — 7.98 trillion yen — to prop up the currency. That is the biggest single-day yen-buying operation on record, blowing past the previous high of 6.28 trillion yen set on April 30, per ministry data going back to 1991.

The buying didn't stop there. Japan spent another 5.55 trillion yen on July 31, a day the US also stepped in by selling euros for yen, followed by 1.87 trillion yen on August 3. The moves came as the yen sank to its weakest level in four decades, hovering near 164 per dollar.

Monday's breakdown fills in the details of the record 15.4 trillion yen ($97.19 billion) monthly intervention run that stretched from July 30 through August 26. It also wasn't a solo act: South Korean officials said at the time that the Bank of Korea timed its own won-buying intervention alongside Japan's to make both packs hit harder.

Tsuyoshi Ueno, senior economist at NLI Research Institute, said the sheer size of the operation made Tokyo's alarm clear. He added that the yen could stay under downward pressure as the forces dragging on it remain unresolved.